Fig. 1

a Location of the study area in Kyushu, southwestern Japan. b Active faults in the western part of central Kyushu (blue lines after Nakata and Imaizumi 2002, light blue lines after ERC, HERP 2013) and the 2016 surface ruptures (red lines). c Distribution of surface ruptures associated with the 2016 Kumamoto earthquake sequence observed during our survey (red lines), previously mapped active faults (blue lines), and the best double-couple solution of centroid moment tensor diagrams for the mainshock and the initial M _J 6.5 event (yellow beach balls) determined by the Japan Meteorological Agency, and unconfirmed ruptures interpreted from aerial photographs (Geospatial Information Authority of Japan 2016c) (dashed red lines)